You work at a credit card company and as a value-add they want to start providing alerts to users when their spending in any particular spending is higher than usual.
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A Payment is a simple value object with a price, description, and spending.
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A Category is an enumerable type of a collection of things like “entertainment”, “restaurants”, and “golf”.
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For a given userId, fetch the payments for the current month and the previous month.
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Compare the total amount paid for the month, grouped by spending; filter down to the categories for which the user spent at least 50% more this month than last month.
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Compose an e-mail notification to the user that lists the categories for which spending was unusually high, with a subject like “Unusual spending of $1076 detected!” and this body:
Hello card user!
We have detected unusually high spending on your card in these categories:
* You spent $148 on groceries
* You spent $928 on travel
Love,
The Credit Card Company
- [R] Probably User should not be a detail or
Notification, insteadAlertSystem#sendshould receiveUserandNotification?